Inspection and control system



Feb. 6, 1962 J. F. LAYCAK ET AL INSPECTION AND CONTROL SYSTEM 5Sheets-Sheet 1 Filed Nov. 25, 1959 INVENTORS Russel L.Uphoff 8 m Y w M uR F 0 T n m wmN M Nwm vmm mmm 7 -3 w 1 wmm Y .0 0 1 I I l. illllllu'Feb. 6, 1962 J. F. LAYCAK ETAL 3,020,034

INSPECTION AND CONTROL SYSTEM Filed Nov. 25, 1959 5 Sheets-Sheet 3 ,IBB

H H MOUMZ INVENTORS Russel L.Uphoff 6 John F.Luycok 71/ TM'H JHV Fig.3

ATTORNE Y 1962 J. F. LAYCAK ETAL 3,020,034

INSPECTION AND CONTROL SYSTEM 5 Sheets-Sheet 4 Filed NOV. 23, 1959 lNVENTORS Russel L. L lphoff a oycak ATTORNEY Feb. 6, 1962 J. F. LAYCAK ETAL3,020,034

INSPECTION AND CONTROL SYSTEM 5 Sheets-Sheet 5 Filed NOV. 23, 1959 5 wkR G Y o o c E T h. V: N P G M W l O F T b 2- m n M m 23.50 w W Y B Q wenn ll nun nu l mhv 0%.? w? W a g ofl w fi a mt 3 2: :4 5 5 o a UnitedStates Patent fiice vania Filed Nov. 23, 1959, Ser. No. 854,908 14Claims. (Cl. 266-43) This invention relates to a method and apparatusfor detecting defects on the surface of a body and for integrating thecombined areas of the defects over a predetermined surface area of thebody to actuate a device for removing the defects when their combinedareas reach a certain limit. More particularly, the invention relates toan inspection and control system utilizing an electron-optics device forelectronically scanning the image of the surface of a body to produce anelectrical signal indicative of the surface condition of the body beingscanned.

Although not limited thereto, the present invention is particularl adated for use with an automatic hot scarf-v ing machine for steel slabs,billets and the like. When steel is hot rolled from the ingot to asemifinished form, a variety of ingot defects and some defects arisingduring heating or rolling may be carried through to appear on thesurface of the semifinished product. Such defects include cracks, scabs,seams and folds. If the more serious of these defects are not at leastpartially removed, they are carried through to the finished form,resulting in an inferior product.

In the usual automatic hot scarfing operation one or more gas cuttingtorches or scarfing heads are located adjacent the respective sides ofan irradiant hot slab or billet as it travels along a conveyor, thearrangement being such that the torches will remove an entire layer ofthe surface of the workpiece as it passes thereby. Generally, thescarfing heads remove about inch from the surface of the workpiece whichis suiiicient to remove the defects referred to above; but since thescarfing heads are operated continuously, the entire surface of theworkpiece is removed, resulting in a 2% or higher metal loss. in a25,000 pound slab, for example, removal of a M inch layer of metal fromall four sides causes a metal loss of about 500 pounds or 2.3% of thetotal weight. This is a wasteful process since only those portions ofthe slab containing defects need be removed. Therefore, it is highlydesirable to remove only the defective portions to thereby decrease themetal loss occurring during the scarfing operation.

The present invention has as its principal object the provision of amethod and apparatus for detecting defects over a predetermined area ofthe surface of a metal workpiece, and for integrating the combined areasof these defects to actuate means for removing the defects when theircombined areas reach a predetermined limit.

More specifically, an object of the invention resides in the provisionof automatic hot scarfing apparatus for removing only the defectiveportions of the surface of an irradiant hot metal body whereby anappreciable increase in yield is achieved. As will become apparent fromthe following description, a hot steel slab is irradiant, meaning thatit glows or gives off light. Furthermore, defects on the surface of theslab appear brighter or darker with respect to the remainder of thesurface. Protrusions appear darker since they are cooler than theremainder of the surface, whereas holes or indentations appear brightersince they are hotter. This factor is utilized in the present inventionin detecting the defects and integrating their total area over a givensector of the surface of the slab.

in accordance with the invention, a photosensitive device such as avidicon is located ahead of a scarfing head along a conveyor and isutilized to scan the image of the body.

the surface of a moving irradiant body along a fixed line extendingsubstantially perpendicular to the direction of movement of the body. Inthis manner, the electron beam of the photosensitive device producesavideo signal in which a relatively long pulse is produced for each scanof the electron beam, this pulse being produced as the beam scans acrossthe image of the irradiant surface of Superimposed on this long pulseare positive or negative short pulses which arise when the electron beamscans over the image of a defect, the width of each pulse beingproportional to the width of the defect it represents. in this manner, apositive pulse is produced when the beam scans over a defect image suchas a hole having a greater light intensity than the remainder of thesurface,

while a negative pulse is produced by a defect image such 7 as a seamhaving a lower light intensity. Means are provided for eliminating allbut the positive and negative short defect pulses in the video Waveshape which are thereafter converted to one polarity. The resultantpulses are then used in an integrating circuit to trigger an oscillatorwhich feeds a high frequency oscillatory signal to a counter only duringthe successive durations of the short pulses in the signal.

It will be apparent that if the electron beam of the photosensitivedevice scans along the aforesaid fixed line at a constant sweepfrequency, the total number of defeet pulses produced for any givenlength of the body will be a function of its speed. That is, if the bodytravels along its conveyor at a high rate of speed, a fewer number ofdefect pulses will be produced during one foot of travel than would beproduced for the same foot of travel if the speed of the body weredecreased. Since it is desired to integrate the widths of the defectpulses over a given length of the body, and since the number of thesepulses is dependent upon the speed of the body, some means must beprovided to insure that the number of defect pulses fed to theintegrating circuitry will be the same for a particular length of thebody regardless of its speed. Otherwise, the output of the integratingcircuitry will not be a true indication of the total defect area. Inaccordance with the present invention, the speed of the body ismeasured, and the repetition rate of the electron beam of the vidicon ismade proportional to that speed. In this manner, the number of defectpulses reaching the integrating circuitry will always be the sameregardless of the speed of the body.

The counter in the integrating circuitry referred to above isessentially a device for producing an output voltage when the total areaof the defects reaches a predetermined limit. That is, when the totalnumber of oscillation fed to. the counter during successive pulseintervals reaches a given amount, the counter will produce an outputvoltage defects in the area surrounding it.

which is used to turnon the scarfing head. Means are also provided forresetting the counter after the body has moved over a certain distance,say, one foot. Thus, if the number of oscillations representing thetotal defect area fed to the counter does not reach the aforesaid givenamount. during one foot of travel, the counter will be reset beforeproducing an output voltage; and that particular one foot length of thebody will not be scarfed. In this manner, in the absence of anexceptionally large protrusion, only those portions of the body having apredetermined total defect area will be scarfed in response to an outputvoltage from the counter.

Another object of the invention is to provide means in a system of thetype described above for removing a defect producing a deep, negativepulse in. the wave form regardless of the total defect area scanned overa particular increment of area of the slab. Such defects might, forexample, be a large scab or other protrusion which must be removedregardless of the total number of Accordingly, the in- Patented Feb. 6,1962 V vention provides means for overriding the usual control circuitryand for actuating the scarfing head when such a defect occurs.

The above and other objects and features of the invention will becomeapparent from the following detailed description taken in connectionwith the accompanying drawings which form a part of this specificationand in which:

FIGURES 1A, 1B and 1C are illustrations of the effect of selectivescarfing as compared with the ordinary scarfing procedure;

FIG. 2 is a block diagram of the overall control system of the presentinvention;

FIG. 3 is an illustration of wave forms appearing at various points inthe circuit of FIG. 2;

FIG. 4 is a detailed schematic diagram of the vidicon sweep controlcircuitry shown in FIG. 2;

FIG. 5 is a detailed schematic diagram of the deundulating and pedestalremoving circuitry shown in FIG. 2;

FIG. 6 is a detailed schematic diagram of the displacement detectorcircuitry shown in FIG. 2;

FIG. 7 is a detailed schematic diagram of the defect integratingcircuitry shown in FIG. 2; and

FIG. 8 is a detailed schematic diagram of the override circuit for deep,negative defects shown in FIG. 2.

General overall description of invention Referring to FIG. 1, itrepresents a slab on which are several scabs 1.2 and a seam 14. FIG. 1Bshows the usual method of hot scarfing used to eliminate the defects.Note that the entire shaded area is scarfed, while only certain portionsof the surface contain defects. This, of course, results in anunnecessary loss of metal as was explained above. FIG. 1C illustratesthe effect of the elective scarfing process of the present inventionwherein only the defective, shaded areas are scarfed while tie remainderof the slab is untouched. It is thus apparent that since only a portionof the surface of the slab has been burned, the metal loss resultingfrom the scarfing operation is appreciably reduced.

Referring to FIG. 2, a slab is illustrated as passing over a series ofconveyor rolls 18. Above the slab is a vidicon tube adapted to scan overa single fixed line which extends substantially perpendicular to thedirection of movement of slab 16. Following vidicon 20 is a scarfinghead 22 which is controlled by means of a valve 24 or other similardevice actuated by an electrical utilization device, such as a solenoid26. Although only one vidicon tube and one scarfing head are illustratedin FIG. 2, it should be understood that a plurality of tubes andscarfing heads could be provided for each side of the slab; and, ofcourse, the control circuitry hereinafter described would have to beduplicated for each tube and scarfing head combination. As illustratedin FIG. 2, one of the conveyor rolls 18 is connected through amechanical linkage to a tachometer 28, although any means could be usedto actuate the tachometer which has a rotational speed proportional tothe linear speed of the slab 16.

The control circuitry of FIG. 2 may be divided into several portions,each of which is enclosed by broken lines. Thus, the block diagramincludes camera sweep control circuitry 30, a displacement detector 32,deundulating and pedestal removing circuitry 34, a defect integrator 36,and an override circuit for deep, negative defects 38. Each of theseportions will hereinafter be described in detail.

Turning now to the camera sweep control circuitry 30, the sine waveoutput of tachometer 28 appearing as wave form A in FIG. 3 is passedthrough a variable gain amplifier 49 to a diode clipping and peakingcircuit 42. Wave form A is also fed to an automatic gain control circuit44 which produces a direct current voltage proportional to the averagevoltage level of the sine wave from tachometer 28. As will beunderstood, both the amplitude and the frequency of the signal output ofthe tachometer increase as slab speed increases. The output of thecircuit 44 is then fed to the variable gain amplifier 4%} to control itsoutput level and insure that the sine wave output of the amplifier willalways be of the same amplitude. The diode clipping and peaking circuit42 removes the negative half cycles of the sine wave from amplifier 4t}and peaks the positive half cycles to produce the wave form B shown inFIG. 3. Further peaking and amplification are achieved in peakingamplifier 46 whose output (wave form C in FIG. 3) is then used toactuate a Schmitt trigger multivibrator 48. The output of triggercircuit 48 will appear as wave form D in FIG. 3 and consists of asuccession of square wave voltage pulses, each of which persists for thetime duration of a peak in wave form C at the output of amplifier 46.The pulses in wave form D are then used to trigger a one-shotmultivibrator 50 which will produce a voltage pulse of fixed width eachtime a pulse is received from circuit 48. The output of multivibrator 56will, therefore, appear as wave form E in FIG. 3. This wave form is fedthrough a cathode follower attenuator 52 and lead 54 to camera controlcircuit 56.

The camera control circuit 56 will produce the sawtooth wave form Fshown in FIG. 3. This Wave form is a series of rising current excursionswhich causes the electron beam of the vidicon to sweep across thesurface of the slab and then return to its initial position during adwell time when the wave form F returns to its initial current level. Itwill be noted that the length of each rising current excursion in waveform F is equal to the width of a pulse in wave form E, this width beingfixed by the one-shot multivibrator St). The length of the dwell timebetween successive current excursions in wave form F, however, dependsupon the spacing between pulses in wave forms B, C and D; and thisspacing, in turn, depends upon the frequency of the sine wave A and thespeed of slab 16. In this respect, it will be apparent that as the slab16 slows down and the frequency of wave form A decreases, the spacingbetween pulses in wave forms B, C and D will increase so that thespacing between pulses in wave form B will also increase. In addition,the dwell time between successive current excursions in Wave form F willincrease, but the time duration of each excursion will remain the samesince this is fixed by the period of one-shot multivibrator 50. Thus,the frequency at which the electron beam of vidicon 2i) sweeps acrossthe image of slab 16 will always be a function of the speed of the slab.

The wave form F is fed to the vidicon 20 through lead 58 while the videowave form, illustrated as wave form G in FIG. 3, appears on lead 69. Asshown in FIG. 3 this video wave form is a series of relatively longpulses having superimposed thereon short pulses indicating the prcsenceof defects. Thus, it will be apparent from FIG. 3 that as the electronbeam sweeps from one side of the conveyor to the other, it will firstscan the dark background portion of the conveyor until it reaches pointa which is the edge of the irradiant slab 16. After intersecting theedge of the slab, the voltage of the video wave form increases becauseof the greater light intensity of the slab. At point [1 the electronbeam intersects a defect 62 having a greater light intensity than theremainder of the slab. Consequently, a positive pulse 64 is produced inthe wave form. At point 0 the electron beam again intersects a defect 66but in this case the defect has a lesser light intensity than theremainder of the slab; and, consequently, a negative short pulse 68 isproduced in the wave form. Finally, at point d in the wave form theelectron beam leaves the edge of the slab and the voltage decreases dueto the dark background of the conveyor. Between points e and f theelectron beam returns to its original starting position over a veryshort interval of time, and the cycle is repeated.

Turning again to P16. 2, from lead 63 the wave form G is passed througha first clipper 7t) and amplifier 72 to a second clipper 74 and a secondamplifier 76. The function of the first clipper 70 is to remove thelower portion of the video wave form G so that only the pulse betweenpoints a and d remains. Circuit 72 amplifies the wave form and clipper74 further refines the clipping action so as to insure that clean pulsesof high amplitude appear at the output of amplifier 76. These pulses,then, appear as wave form H in P16. 3. This wave form is passed throughstill another amplifier 78 to a difierentiator 81 which produces a sharpspiked pulse of positive polarity whenever the input wave form H changesin a positive direction and a sharp spiked pulse of negative polaritywhenever the input signal level changes in a negative direction. Theoutput of the diiierentiator thus appears as wave form I in FIG. 3. Thiswave form'is fed to a pulse separation circuit 32 which separates thepositive pulses in wave form I from the negative pulses. The negativespiked pulses are fed through amplifier S4 wherein they are inverted toappear as the positive pulses in wave form I of FIG. 3. In a similarmanner, the positive spiked pulses from separation circuit 82 are fedthrough amplifier 86 and phase inverter 88 such that the pulses in waveform K appearing at the output of the phase inverter correspond to theoriginal positive spiked pulses in wave form 1. The spiked pulses inwave forms J and K are then fed to a mixer 90 Where they are combined toproduce a series of positive spiked pulses in wave form L, with eachpulse corresponding to the leading or trailing edge of a pulse in waveform H. The net effect of circuits 829fi, therefore, is to convert allof the spiked pulses in wave form I to one polarity. These spiked pulsesare then passed through amplifier 92 and phase inverter 94 to a lategate circuit 96.

From an examination of wave form L in FIG. 3, it will be seen thatspiked pulse 98 corresponds to the leading edge of the pulse produced atpoint a when the electron beam strikes the edge of the slab, whilespiked pulse 1% is that produced when the electron beam intersects theother edge of the slab at point of. Pulses 1612 and 104, however,correspond to the leading and trailing edges of the pulse 64- producedby defect 62; while pulses 106 and ithi correspond to the leading andtrailing edges of the pulse as produced by defect 66. It is desired tointegrate only the distances between the respective spiked pulsesoriginating at the leading and trailing edges of pulses 64 and 68produced by defects, such as the distance between pulses 102'and 104 andthat between pulses 1G6 and 1118. Consequently, the pulses 98 and 100clue to the leading and trailing edges of the relatively long pulses inthe video wave form must be eliminated.

To this end, circuitry is provided including an ampliher 110 to whichwave form H from amplifier 76 is fed. The output of amplifier 110 isdivided between two channels 112 and 114. Channel 112 includes a cathodefoilower stage 116, a delay line 118, amplifier 120, Schmitt triggercircuit 122, and phase inverter 124; After passing through delay line118, the video wave form is delayed by /2 microsecond and appears aswave form M in FIG. 3. The delayed wave form, after passing throughamplifier 129, is used to trigger the multiviorator or Schmitt triggercircuit 122 so that the output of phase inverter 124 appears as waveform N which is a series of pulses all having a width proportional tothe width of the slab 16, but delayed by /2 microsecond with respect tothe original video wave form. The wave form N is then passed to the lategate 96 along with wave form L from phase inverter 94. Late gate 96 willproduce an output signal when, and only when, there is a coincidence ofpulses in Wave forms N and L. F-rom an inspection of these wave forms inFIG. 3 it will be seen that they coincide to pass all pulses exceptpulse 98 due to the leading edge of the slab 16. The /2 microseconddelay imparted by delay line 118 is just enough to eliminate this pulseand, of course, should be kept as small as possible so as not toeliminate any defect pulses which might occur veryand amplifier 128 toan early gate 13%. The wave form P arriving at the early gate 139 is asshown in FIG. 3

wherein all of the original spiked pulses in wave form L except pulse 98remain.

The output of amplifier in channel 114 is first fed through a Schmitttrigger multivibrator 132 which produces wave form Q at the output ofphase inverter 134. The wave form Q and wave form P from amplifier 128are fed to the early gate 136 which functions in a manner similar togate 96 in that it will pass output signals only upon coincidence of apulse in wave form Q with one in wave form P. it can be seen from FIG. 3that since wave form P has been delayed by /2 microsecond while waveform Q has not, the spiked pulses 16% extend beyond the trailing edgesof the pulses in wave form Q and, there-j fore, do not appear at theoutput of early gate 130. The wave form R at the output of early gatewill, therefore, be only the spiked pulses 1d21il8 produced by theleading and trailing edges of the defect pulses 64 and 68 in theoriginal video wave form G. These pulses are fed through amplifier 136to a flip-lop or multivibrator 138 which is alternately triggered on andoil by successive spiked pulses from amplifier 136. Thus, the output offiip'flop 138 appears as wave form S in FIG; 3 and comrises a series ofdelayed pulses each of which has-a phase position and pulse widthcorresponding to the original defect pulses 6d and 68 in the video waveform.

Wave form S comprising pulses 1% and 142 is then passed to gatingcircuit 144 which couples the output of a high frequency oscillator 146to a phase inverter 148 and peaking amplifier 159 only during the timeduration of pulses 14d and 142 from fiip-flop circuit 138. Thus, theoutput of peaking amplifier 156 will appear as wave form T whichcomprises short periods of oscillation from oscillator 146 correspondingin phase and width to pulses 14d and 1 52. The oscillations in wave formT are passed through a series of decade counters 152, 154, etc. When thenumber of oscillations which are permitted to pass through gate 144reaches a predetermined number, the last decade counter 156 will producean output voltage on lead 158 which is fed to a memory device 160 whichmay, for example, comprise magnetic tape apparatus. After a specifieddelay period, the memory circuit 160 then passes the voltage produced bydecade counter 156 through a scarier control circuit 162 which actuatesthe electrical utilization device 26 to turn on scarfing head 22 for apredetermined length of the slab, which length is determined by a camoperated switch or other similar device connected to the shaft oftachometer 28.

Wave form E at the output of cathode follower 52 is applied not only tocamera control circuit 56 but also to a series of binary countingcircuits'164, 166, etc. When a predetermined number of the pulses inwave form E are fed to the binaries, the last binary 168 will produce anoutput voltage which triggers one-shot multivibrator 170 to produce apulse of fixed duration which is passed through a cathode follower, notshown, and lead 172 to each of the decade counters 152, 154, 156, etc.This pulse serves to reset each of the counters, meaning that if thetotal chain of counters is adapted to count a million oscillationsbefore producing an output voltage and only a part of the millionoscillations have been fed to the counter before the pulse on lead 172is produced, then another million oscillations will have to be fed tothe counter before it will produce an output voltage on lead 15%. 7

It will be noted that the output of tachometer 28 is also fed to arectifier 174, the output voltage of which is passed through a directcurrent amplifier or reset generator 176 to a relay 178. This relay,acting, through U lead 180, resets the binaries 164-163 in response to adirect current voltage from rectifier 174. Thus, when the leading edgeof the slab 16 causes the roller connected to tachometer 28 to rotate,the binaries will be reset, insuring that counting begins at theaforesaid leading edge.

The output of amplifier 7?, appearing as wave form H in FIG. 3 is alsoapplied through lead 182 to a Schmitt trigger circuit or multivibrator186 which will shift from one stable state to another when the inputvoltage exceeds a predetermined triggering level. This voltage isapproximately that shown by dotted line 188 in PEG. 3 so that themultivibrator 186 will turn on and off in response to the leading andtrailing edges of each long pulse in the wave form H. These pulses arethen fed to a one-shot multivibrator 19% which will produce outputpulses in response to the pulses from multivibrator 186, with the pulsesin this case having a fixed pulse width which is not dependent upon thewidth of the pulses in original wave form H. The output of multivibrator190 is then fed through variable gain amplifier 192 to an integrator 196which produces an output voltage which is a direct function of the totalpulse area per unit of time of the input pulses applied thereto. Whenthe output voltage from integrator 196 reaches a predetermined value, itwill trigger Schmitt trigger 198 and multivibrator 299 to produce anoutput voltage pulse which is fed to the memory circuit 169. Thisvoltage, then, will actuate the scarfing head 22 through circuit 162 inthe same manner as an output voltage from the counter on lead 153.

If a negative voltage pulse in the video wave form G, such as pulse 68,is exceptionally large, it will extend below the triggering level 188 ofmultivibrator 136. Thus, instead of producing one output pulse for eachsweep of the electron beam, the multivibrator will produce two pulsessince it will be turned on and off twice during the sweep period.Consequently, the recurrence of the pulses during each sweep intervalwhich are now fed to integrator 196 is doubled, and its output voltageis raised due to an increase in the total pulse area per unit of time.Although the frequency of the pulses fed to integrator 196 will increasein the manner described above in response to a deep, negative defect, itwill also increase in response to an increase in slab speed. Thisincrease will affect the voltage produced by integrator 196; and sinceit is necessary that the voltage output of the integrator be a functionof the presence of deep, negative defects only, some means must beprovided to compensate for the increase in slab speed. To this end, anautomatic gain control circuit 2531 is included in the circuit whichrectifies the output of tachometer 23 and applies it to variable gainamplifier 192 as an automatic gain control voltage. In this manner thegain of the amplifier is reduced as the amplitude of the sine waveoutput of tachometer 28 increases, and the voltage produced byintegrator 196 is held constant as the slab speed increases. Thus,integrator 196 will increase its output voltage to the point where ittriggers circuits 198 and 200 when, and only when, an exceptionallydeep, negative pulse is produced in wave form G so as to increase thenumber of the pulses fed to integrator 196 during each sweep of theelectron beam.

Operation of the system As long as the lectron beam of vidicon 20 sweepsover defects on the surface of the slab 16, wave form S will be producedat the output of flip-flop circuit 138. This wave form will appearregardless of the speed of the slab 16 just so long as the electron beamscans a defect. Of course, the frequency of the pulses in wave form Swill be a function of the speed of the slab. Thus, if the speed of theslab were doubled over that assumed for the wave forms given in FIG. 3,then twice the number of pulses would appear in wave form S.Consequently, as the slab travels through a one-foot interval,

the number of pulses reaching gate 144 will be the same for a giventotal defect area regardless of the speed of the slab 16, the onlydifference being that if the speed of the slab is increased, the timeinterval required for the given number of pulses to arrive at gate 144is decreased. It will also be apparent that the number of oscillationsfrom oscillator 146 arriving at the counters 152, 154, etc. will alwaysbe the same for a given defect area regardless of the speed of the slab.

The present invention is constructed and arranged such that the scarfercontrol 162 will ordinarily be actuated only when the total integrateddefect area over one foot of the length of the slab 16, for example,reaches a predetermined value. In this respect the counters 164, 166,etc. will provide an output pulse to reset the counters 152, 15d, etc.after the slab has traveled a predetermined distance so that if anoutput pulse does not appear on lead 158 after the slab has traveled thepredetermined length, then it will be necessary to integrate the defectsappearing on the next unit of length of the slab to determine if theirtotal area is great enough to actuate the scarfer control.

As was stated above, the wave form E is fed to the binary counters 16 i,166, etc. If it is assumed that there are twelve binaries connected inseries, then 4,096 pulses in wave form E will have to be fed to thebinaries before an output pulse is produced on lead 172 to reset thecounter in circuit 36. If the tachometer 28 is selected to produce 4,096cycles of oscillation during one foot of travel of the slab 16, it willbe apparent that a pulse will appear on lead 172 for each foot of travelof slab 16. Furthermore, the counters 152, 154, etc. will be reset aftereach foot of travel of the slab so that if a predetermined number ofoscillations from oscillator 146 are not fed to the counters 152, 154,etc. during the one foot of travel, then the scatter control 162 willnot be actuated. Thus, the scarfing head operates during one-footintervals and may or may not be actuated during any particular one-footinterval, depending upon the number of oscillations fed to counters 152,154, during that one-foot interval; and this number is, of course, afunction of the total defect area appearing on the surface of the slabover the one foot.

Notwithstanding the above, when a negative pulse in the video wave form,such as pulse 68, extends below the triggering level 188 of Schmitttrigger 186 due to a deep, negative defect, the number of pulses duringeach sweep interval fed to integrator 196 will increase. This increasewill raise the output voltage of the integrator 196 to trigger circuits198 and 200 and produce an output voltage which is applied to the memorydevice 160. Thus, where a deep, negative defect appears, the scarfinghead 22 will be actuated even though the number of oscillations fed tocounters 152, 154, etc. is not great enough to produce an output voltageon lead 158.

Detailed description of circuits Referring to FIG. 4, the vidicon sweepcontrol circuitry identified by the numeral 38 in FIG. 2 comprises alead 202 on which the sine wave output of tachometer 23 (wave form A) isapplied. The sine wave is applied through capacitor 204 and a voltagedivider consisting of resistors 236, 297 and 208 to the control grid 210in the pentode 212 of variable gain amplifier 44). The automatic gaincontrol circuit 44 comprises a diode rectifier 214 and smoothingcapacitors 216, 218 which apply a direct current voltage to control grid210, this voltage being proportional to the average voltage amplitude ofthe sine wave input from the tachometer. Since the amplitude of the sinewave from the tachometer will increase as its speed increases, theautomatic gain control circuit, by feeding a negative voltage to grid210, will automatically compensate for this increase to maintain theoutput of amplifier 40 at a substantially constant amplitude. The outputof amplifier 40 on lead 219 is fed to the diode clipping and peakingcircuit 42 which comprises a diode 220 having its cathode connected toground through resistor 222. In this manner, the negative half cycles ofthe sine wave appearing at the plate of pentode 212 are eliminated.Diode 224 in circuit 42 is a peaking diode for producing pulses thatoccur at the peak of the half sine wave leaving diode 220. This waveform (wave form B in FIG. 3) is then applied to peaking amplifier 46which comprises two series-connected triodes 226 and 228, with theoutput of triode 226 being coupled to the grid of triode 228 through anRC network consisting of capacitor 238 and resistor 232. The output ofpeaking amplifier 46 will appear as wave form C in FIG. 3. This waveform is applied through capacitor 236 and resistor 238 to the Schmitttrigger multivibrator 48 which comprises a pair of triodes 240 and 242having their cathodes connected to ground through a common resistor 246.It'will be noted that the anode of triode 248 is connected to the gridof triode 242 through the parallel combination of capacitor 248 andresistor 25!).

Under normal conditions triode 242 will conduct while triode 248 will becut 05. When the positive pulse in wave form C is applied to the grid oftriode 240, however, it will begin conduction when the pulse in waveform C reaches a predetermined amplitude. Conduction in tube 248 willcut off triode 242 because of the fall in the plate voltage of triode240 which is coupled to the grid of triode 242 through elements 248 and250. Triode 243 will continue to conduct until the voltage level of thepulse in wave form C falls below the aforesaid predetermined amplitude,at which time it will cut oif and triode 242 will again conduct. Theoutput appearing at the plate of triode 242 is, therefore, wave form Dwhich comprises a series of positive square wave pulses each of whichhas a pulse width slightly smaller than the width of the pulse in waveform C which was fed to the grid of triode 240.

The output of the Schmitt trigger 48 on the plate of triode 242 is fedto the one-shot multivibrator 58 comprising a pair of triodes 252 and254 having their cathodes connected to ground through a common cathoderesistor 256. As shown, the anode of triode 252 is connected to the gridof triode 254 through capacitor 258 having one of its terminalsconnected to a 13+ voltage source through resistor 260. Under normalconditions, triode 254 will conduct while triode 252 is cut ofi. When,however, a positive pulse at the output of Schmitt trigger 48 is appliedto the grid of triode 252, this triode will conduct and its platevoltage will fall. The fall in plate voltage is thus applied to the gridof triode 254, causing it to cut off. After a predetermined period oftime determined by the values of capacitor 258 and resistor 268, thecharge of the capacitor will leak off and triode 254 will again conduct.In this manner an output pulse of fixed duration will appear at theoutput of multivibrator 58 for each cycle of the sine wave produced bytachometer 28. The signals on the plate of triode 254 are applied to thegrid of triode 262 in cathode follower stage 52, and the output of thisstage at the cathode of triode 262 is applied to the camera controlcircuit 56 as well as the binaries 164, 166, etc. in circuit 32. As wasexplained above, the electron beam of vidicon 20 will be caused to sweepacross the image of the surface of slab 16 during the persistence ofeach pulse in wave form E at the output of cathode follower 52. Althougheach pulse in wave form E is of the same width regardless of the speedof slab 16 and the frequency output of tachometer 28, the spacingbetween the pulses in wave form E will be inversely proportional to slabspeed while the sweep recurrence frequency of the vidicon will bedirectly proportional to slab speed.

The deundulating and pedestal removing circuitry identified by thenumeral 34 in FIG. 2 is shown in detail in FIG. 5. The video input onlead 60 appearing as wave form G in FIG. 3 is applied to the clipper70-which comprises a diode 274 having its cathode connected to groundthrough resistor 276 and capacitor 278. The voltage level at the cathodeof diode 274 is adjusted by a potentiome ter 280 whereby the bottomportion of the wave form is removed. In actual practice the portionremoved corresponds to that below the pedestal produced between the twosides'of the slab 16. That is, only the portion of the wave form betweenpoints a and d remains. From clipper 70 the wave form G is passedthrough amplifier 72 which comprises a pair of triode tubes 282 and 284connected in series. The output of triode 284 is clamped by diode 286and passed to clipper 74 which comprises a a diode 288 having itscathode connected to ground through resistor 290 and capacitor 292. Aswas the case with diode 274, the cathode potential of diode 288 isadjusted by means of voltage divider 294. The outputof the clipper '74-is passed through amplifier 76 which, like amplifier 72, comprises apair of series-connected triodes 296 and 298. The output of amplifier 76is fed to amplifier 78 which also comprisesa pair of series-connectedtriodes 308 and 302. In this case, the anode of triode 300 is connectedthrough lead 182 to Schmitt trigger 186 (shown in FIGS. 2 and 8);whereas, triode 302 is connected in cathode follower relationship to thedifferentiator 88 comprising inductor 304 and resistor 306. As is wellknown'to those skilled in the art, a differentiator is a circuit inwhich the voltage amplitude at the output is approximately proportionalat any instant to the rate of change of voltage amplitude at the input.The voltage wave form appearing at the output of the differentiator(wave form I) will, therefore, be a series of sharp voltage pulses whichoccur in time at the points where the input signal abruptly changes fromone voltage level to another. Thus, a sharp voltage pulse will beproduced in wave form I at the leading and trailing edge of each pulsein wave form H. It will be noted that the sharp pulses produced whenwave form H changes in a positive direction are positive, while thesharp pulses produced when the wave form changes in a negative directionare negative.

The pulse separator circuit 82 comprises a pair of diodes 388 and 310.It will be notedthat the polarities of these diodes are reversed. Thus,diode 388 will pass positive pulses in wave form I to lead 312; whereasdiode 310 will pass negative pulses in the wave form I-to lead 314. Thesignals appearing on leads 312 and 314 are, therefore, the positive andnegative halves, respectively, of wave form I. The signal on lead 314 isapplied to the amplifier 84 which comprises a single triode tube 316.Since the original signal fed to the grid of triode 316 had negativepulses therein, the pulses appearing at its anode and on lead 320 willbe positive. Ina similar manner, positive pulses passing through diode308, when applied to the grid of triode tube 322' in amplifier 86, willproduce negative pulses at the plate of this triode which are fed to thegrid of triode 324 in phase inverter 88 so that the pulses appearing atits plate are again positive. These positivepulses on lead 326 areapplied to the control grid of a pentode tube 327 in the mixer 90. Theoutput of triode 316 on lead 320 is applied to the suppressor grid ofthis same pentode 327, and since the pulses on leads 320 and 326 are nowboth positive, the output of pentode 327 will be the combined wave formsI and K. p

The signal on. lead 328 is then fed to a plurality of pentodes 330, 332and 334 connected sequentially in am- I plifier 32 which produces waveform L shown in FIG. 3.

The output of the last pentode 334 is applied through 346 and 348connected sequentially in amplifier 110. The output of amplifier 110 ispassed through cathode follower 116 comprising triode 350 to the /2microsecond delay line 118, with the output of the delay line being fedto amplifier 120. As shown, this amplifier comprises a pair of triodes352 and 354 connected in sequence. The anode of triode 354 in amplifier120 is connected to the Schniitt trigger 122 which includes two triodes355 and 357 and which operates in the same manner as the Schmitt triggeralready described. The output of the Schmitt trigger 122 appearing aswave form N is fed through the phase inverter 124 comprising triode 356to the control grid of a pentode 366 in the late gate circuit 96.Amplified wave form L on lead 344 is applied to the anode of pentode 360which is normally conducting to apply a negative bias to the anode ofdiode 362. Thus, the diode will not conduct to pass signals on lead 344as long as pentode 360 is conducting. When inverted wave form N at theoutput of phase inverter 124 is applied to the control grid of pentode360 with a negative polarity, however, the pentode will be cut off, thepotential at the anode of diode 362 will rise, and the diode willconduct to pass signals through triode 364 which has its cathodeconnected to the delay line 126. The output of the delay line, appearingas wave form P, is then applied through lead 366 to the grid of a firstof a pair of seriesconnected triodes 363 and 3'70 in amplifier 128.

It will be noted that the output of amplifier 110 at the plate of triode348 is applied through lead 372 to the grid of the first of two triodes374 and 376 in the Schmitt trigger 132. The output of the Schrnitttrigger 132, appearing as wave form Q in FIG. 3, is applied throughphase inverter 134 consisting of triode 378 to lead 380 where thesignal, appearing as inverted wave form Q in FIG. 3, is applied to thecontrol grid of pentode 382 in early gate circuit 130. The early gatecircuit operates in a manner similar to that of the late gate 96 andineludes a diode 384 which has its anode connected to the anode of thepentode 382. Since the pentode is normally conducting, the voltage atthe anode of diode 384 will be negative with respect to its cathode soas to cut on. the diode. When, however, inverted wave form Q is appliedto the grid of pentode 382, the pentode will cut E and the diode 384will conduct to pass wave form R on the plate of triode 370 in amplifier128 to amplifier 136 which comprises sequentially-connected triodes 386and 388. The output of amplifier 136 on lead 390 is then fed through apentode 392 which inverts the signal and feeds it through lead 394 tothe grids of the two triodes 396 and 398 in flip-flop circuit 138. i

It can be seen that the cathodes of triodes 396 and 398 are bothconnected to ground potential through a single resistor 400. The plateof tube 398 is connected to the 13+ voltage source through resistor 402,whereas the plate of tube 396 is connected to the same source of voltagethrough resistor 404. The grid of tube 396 is connected to groundthrough resistor 496 and to the B+ voltage source through resistors 467and 402 with resistor 407 being bypassed by capacitor 409. In a similarmanner, the grid of tube 398 is connected to ground through resistor 408and to the 3-}- voltage source through resistors 410 and 404, withresistor 410 being bypassed by capacitor 412. It should be noted thatthe plate of triode 396 is connected to the grid of tube 398 throughcapacitor 412 and resistor 410. Likewise, the plate of the tube 398 isconnected to the grid of tube 396 through capacitor 409 and resistor407.

When a source of anode voltage is applied to the flip flop circuit,current will tend to flow in the plate circuits of triodes 396 and 398.It the two halves of the circuit are identical, the tube currents willbe nearly equal at first. However, a perfect balance is alwaysimpossible; and means are provided to insure that triode 396 initiallyconducts more heavily than triode 398. The increased current in triode396 causes an increase in the voltage drop across resistor 404 and,thus, a decrease in the plate voltage of tube 396. Because of theconnection between the plate of triode 396 and the grid of triode 398,the decrease in the plate voltage of triode 396 is accompanied by adecrease in the grid voltage of triode 393. Therefore, an increase inthe plate current of tube 396 must be accompanied by a decrease in theplate current of tube 398 since its grid is now driven negatively.Moreover, the decrease of plate current through tube 393 causes anincrease of the grid voltage of triode 39-6, and consequently, resultsin a further increase of plate current through triode 396. In thismanner, a slight initial unbalance sets up a cumulative or regenerativeswitching action which reduces the plate current of tube 398 to zero andincreases the plate current of tube 396 to a maximum. Though describedas if it occurred slowly, this switching action occurs with extremerapidity-in a fraction of a microsecond in most flip-iop circuits.

The pulses 102, 104, 106 and 108 in Wave form R on lead 394 are appliedto the grids of triodes 396 and 398 through di0des414 and 416. If triode396 is conducting, these pulses which are negative on the plate ofpentode 392 and lead 394, cut ofi the triode 396. This causes aregenerative switching action in which, while triode 396 cuts off,triode 398 conducts. Furthermore, triode 393 will continue to conductuntil the next pulse is received which is pulse 104 in wave form R. Thispulse will now out oft" tube 398 and will again initiate conduction intriode 396. The result is that a pulse between the spiked pulses 132 and164 in wave form R is produced on lead 418 as wave form S (inverted) in1 16.3.

Referring to FIG. 6, the displacement detector circuitry identified bythe numeral 32 in FIG. 2 comprises the rectifier 174 which includes adiode 426 and a pair of smoothing capacitors 428 and 430. The output ofthe rectifier 174, which is a direct current voltage, is fed to thecontrol grid of a pentode vacuum tube 432 in the reset generator 176.The plate circuit of pentode 432 includes the energizing coil 434 of therelay 178 which is normally deencrgized whereby its contacts 436 areopen. When, however, the tachometer 28 is rotating, and an alternatingcurrent voltage applied to the rectiher 174, the resulting directcurrent voltage on the grid of pentode 432 energizes coil 434 to closecontacts 436.

Also included in the displacement detector are thirteencascade-connected binary counters or flip-fiop circuits 164, 166, etc.,which are similar in construction to the flip-flop circuit alreadydescribed. Each binary comprises a pair of triodes 438 and 440 havingtheir cathodes connected through a common resistor 442 and capacitor 444to ground. The grid of triode 438 is connected through capacitor 446 tothe plate of triode 440; and similarly, the grid of triode 440 isconnected through capacitor 448 to the plate of triode 438. In thismanner, only one of the two triodes will conduct while the other triodeis cut off. Reverting again to relay 178, it will be seen that when itscontacts 436 are closed, the grid of the left-hand triode in each of thethirteen binaries, namely, the grid of triode 438 in binary 164, isconnected to ground through leads 450 and 452. The grid of theright-hand tube in each binary, namely, the grid of triode 440 in binary164, is always connected to ground through resistor 454 so that triode440 will normally conduct. The output of cathode follower 52 on lead455, namely, wave form E of FIG. 3, is simultaneously applied to thegrids of triodes 438 and 440 in the binary 164, while the output of thisbinary is simultaneously applied to the grids of the triodes in the nextbinary and so on to produce a cascade arrangement. The pulses in waveform E as applied to the binary 164 have positive polarities; and, thus,if it is assumed that triode 440 in binary 164 is conducting, the pulseon lead 455, having a positive polarity, will initiate conduction intriode 438 while cutting off triode 440. Triode 438, however, will becut off and triode 446 will conduct when the next successive pulse inwave form E is received on lead 455. Thus, a single negative pulse willbe produced at the plate of triode 438 and passed to the second binaryin the system for each two input pulses on lead 455. In order for asecond pulse to appear at the plate of triode 438, another two pulseswill have to be applied via lead 455. Thus, before the second binarywill produce an output pulse, four pulses must appear on lead 455; and,similarly, before the third binary will produce an output pulse, eightinput pulses must appear on lead 455. In order for the twelfth binary toproduce an output pulse, 4,096 pulses must have been applied to theoriginal binary 164 from lead 455. The output pulse from the twelfthbinary may be applied through lead 456 and switch 458 to the controlgrid of a triode tube 460 in the one-shot multivibrator 170.

The one-shot multivibrator 170 is somewhat similar to the binaryfiipfiop stages just described except that it does not shift from onestable state to another, but rather has only one stable state which maybe interrupted by an input pulse to produce an output pulse of fixedpulse width. Thus, the multivibrator 170 includes the two triodes 460and 462 each of which has its cathode connected to ground through acommon resistor 464 and capacitor 466. In this case, however, the plateof triode 46(l'only is connected to the grid of triode 462 throughcapacitor 468. Under normal conditions tube 469 will conduct while tube462 is cut off. When, however, an output pulse from the twelfth binarystage 168 is applied to the grid of triode 466, the triode will cut offand its' plate voltage will rise. This plate voltage will be appliedthrough capacitor 468 to the grid of triode 462, causing this lattertriode to conduct. After a predetermined period of time the charge oncapacitor 468 will leak off, whereupon the triode 462 will cut off, andsince the pulse on the grid of triode 460 persists for a relativelyshort time, it will again conduct until the next successive pulse isapplied to its grid. If switch 453 is reversed so that the grid oftriode 460 is connected to lead 470, rather than lead 456, then anadditional thirteenth binary 472 will have been inserted into thecircuit, which means that twice the number of pulses on lead 455 willhave to be counted before an output pulse is supplied to the grid oftriode 460. If the number of pulses counted by the first twelve binarycircuits represents one foot of travel of the slab 16, for example, thenthe number of pulses counted when the binary 472 is inserted into thesystem represents two feet of travel.

The output of the one-shot multivibrator 170 appearing on the plate oftriode 462 is applied via clamping diode 474 to the grid of a triodetube 476 in the cathode follower stage 477. The output of this cathodefollower on lead 172 is a pulse which occurs once during each countingperiod of the displacement detector 32. That is, if switch 458 isconnected to lead 456 so that the binaries count 4,096 pulses in waveform B, then a pulse will be produced on lead 172 for each 4,096 pulsesin the wave form E. Similarly, if switch 458 is connected to lead 470,then twice the number of counts or 8,192 pulses will have to be fed tothe displacement detector 32 on lead 455 before an output pulse isproduced on lead 172. This output pulse is used to reset a plurality ofdecade counting units in the defect integrator, hereinafter described.

Referring to FIG. 7, the defect integrator, identified by the number 36in FIG. 2, comprises the gating circuit 144 which includes a pentodevacuum tube 478 having the output of flip-flop circuit 13% applied toits suppressor grid via lead 486. This output appears as wave form S inFIG. 3 and comprises a train of short pulses indicating the existence ofa defect. It will be noted that each pulse 145 and 142 in wave form Shas a pulse width corresponding to the'width of the defect which itrepresents. The pentode tube 478 is essentially a mixer having theoutput of the one megacycle oscillator 146 applied to its control grid.As shown, the oscillator includes a pentode 4'75 and a tank circuit 481.Thus, the wave form appearing at the plate of pentode 478 will be waveform T shown in FIG. 3 which comprises short bursts of oscil lation fromoscillator 146, these short bursts of oscillation extending for. thepulse duration of each pulse in wave form S.

The output of the gating circuit 144 is applied via lead 482 to thecontrol grid of a triode 454 in the phase inverter 148. The output oftriode 484 appearing on its plate is then applied to the control grid ofa pentode 486 in peaking amplifier 150. The output of this amplifier isthen fed to the series of decade counters 152, 154, etc. which producean output pulse on leads 488, 490, 492 and 494 only after apredetermined number of oscillations are supplied to the counter frompeaking amplifier 150. Obviously, the number of pulses required toproduce an output pulse on lead 488 is less than that required toproduce an outputpulse on lead 490. Similarly, the number ofoscillations required to produce an output pulse on lead 492 isgreaterthan that required to produce an output pulse on lead 494 By means ofswitch 4%, any one of the respective leads 488494 may be connected tolead 158 which leads to the memory circuit 160 and scarfer control 162shown in FIG, 2. Thus, the scarfing head 22 may be made to operate inresponse to an output pulse on lead 153 for various numbers ofoscillations from oscillator 146. Since the number of oscillations is adirect function of the total defect area along a predetermined length ofthe slab, the defect area required to actuate the scarfing head maylikewise be varied by changing the position of switch 4%.

It will be remembered that a pulse was produced on lead 172 by thedefect integrator shown in FIG. 6 only after the slab had moved apredetermined distance along conveyor 18. Thus, every time a pulse isapplied to lead 172 to reset the counters 152, 154, etc., the slab willhave moved a predetermined distance. If the total number of oscillationsfrom oscillator 146 representing the total defect area over theaforesaid interval of length does not reach the number required toproduce an output pulse on lead 158, then the scarfer head 22 is notactuated, and the length of the billet represented by the distancebetween pulses on lead 172 is not scarfed. If it .is desired to manuallyreset the decade units 152, 154, etc., switch 4% will be transferredfrom contact 495 to contact 497 whereby the push-button switch 499 maybe depressed to reset the circuitry.

Referring to FIG. 8, the override circuitry for deep,

negative defects represented by the numeral 38 in FIG. 2

comprises the Schmitt trigger 186 which includes triodes 49.8 and 500.This circuit operates in the same manner as the previous Schmitt triggerdescribed. That is, it

will produce an output square wave pulse having a pulse widthcorresponding to the time duration of that portion of an input signalabove a predetermined triggering level. The wave form H shown in FIG. 3is applied to the grid of triode 498, and the threshold value of thistube is adjusted by potentiometer 5M to the position indicated by theline 188 in FIG. 3. Thus, the Schmitt trigger 186 will produce an outputpulse for each pulse extending between points a and d in the wave formH, assuming that the pulse 68 due to a negative defect does not extendbelow the threshold voltage level represented by line 188. If the pulsedoes extend below this threshold level, then the circuit 186 willbetriggered twice during the period of each pulse between points a and d,and the frequency of the pulses at the output of circuit 186 will beeffectively doubled.

The output of Schmitt trigger 186 on the plate of triode 560 is passedto one-shot multivibrator 190 which includes a pair of triodes 504 and566 and which operates in the manner previously described. Consequently,the multivibrator 190 will produce an output pulse of fixed pulse widthfor each input pulse applied thereto from the Schmitt trigger 13 Coupledto multivibrator 190 is the amplifier 392 which comprises a pentode 508having the input signal applied to its control grid. The automatic gaincontrol circuit 201 includes a rectifier G1 and smoothing capacitors 5&3and 595. The output of tachometer generator 23 is applied through thisrectifier and capacitors 5t)?! and 505 to the control grid of pentodc50S whereby, as the speed of the slab and the amplitude of the output oftachometer 23 increase, the gain of amplifier 192 is decreased. Theoutput of pentode 508 is then applied through capacitor Sltl tointegrator 196 which comprises a diode 512 and capacitor 514 connectedin series between the opposite ends of a resistor 516. When pulses arereceived from amplifier 192, they will pass through diode 512 in theforward direction which thus presents a low impedance. Capacitor 514 is,therefore, charged rapidly. On the other hand, the discharge current ofthe capacitor must flow through the high reverse impedance of the diode.Thus, the integrator will produce a steady output voltage having amagnitude proportional to the integrated area of the applied inputpulses.

If, however, the frequency of the input pulses is doubled due to thepresence of a deep, negative defect represented by the pulse 68, thenthe Schmitt trigger 198 will be actuated whereby the triode 526 willproduce a voltage to trigger multivibrator 260 which includes two triodetubes 528 and 53%. The output of multivibrator 206 on lead 532 is thenapplied to the memory circuit 168 and scarfing control circuit 162 toactuate the scarfing head 22 when the deep, negative defect appears inthe video wave form G regardless of whether the number of oscillationscounted in defect integrator 36 are great enough to normally produce anoutput voltage on lead 158.

Although the invention has been shown in connection with a certainspecific embodiment, it will be readily apparent to those skilled in theart that various changes in form and arrangement of parts may be made tosuit requirements without departing from the spirit and scope of theinvention. In this respect the entire circuitry shown in FIGS. 4-8 couldbe transistorized to replace the vacuum tubes shown herein.

We claim as our invention:

1. In apparatus for detecting flaws on the surface of moving material inwhich the flaws have a different optical appearance than the remainderof the material, the combination of means including an electron-opticsdevice for scanning an image of the surface of said moving material at asweep repetition frequency which varies as a function of the speed ofsaid moving body, means responsive to the output of said electron-opticsdevice for producing a pulsed signal in which each pulse has a widthproportional to the width of a flaw image scanned by said electron beam,and apparatus coupled to said latter-mentioned means for integrating thepulses in said pulsed signal to produce an indicating voltage when thesum of the widths of the pulses in said signal reaches a predeterminedamount.

2. In apparatus for detecting flaws on the surface of moving material inwhich the flaws have a different optical appearance than the remainderof the material, the combination of means including an electron-opticsdevice for scanning an image of the surface of said material with anelectron beam along a line extending substantially perpendicular to thedirection of movement of the material, means connected to saidelectron-optics device and responsive to the speed of said material forcontrolling the electron beam of the electron-optics device whereby ithas a sweep repetition frequency proportional to the speed of thematerial, means responsive to the output of said electron-optics devicefor producing a pulsed signal in 1% which each pulse has a widthproportional to the width of a flaw along said scanning line, and meanscoupled to said last-named means for integrating the widths of thepulses in said si nal to produce an indicating voltage when the sum ofthe widths in said signal reaches a predetermined amount.

3. In apparatus for detecting flaws on the surface of moving material inwhich the flaws have a different optical appearance than the remainderof the material, the combination of means including an electron-opticsdevice for scanning an image of the surface of said body with anelectron beam at a sweep repetition frequency proportional to the speedof the moving material, the scanning line of the electron beam beingsubstantially perpendicuar to the direction of movement of the material,means responsive to the output of said e1ectronoptics device forproducing a pulsed signal in which each pulse has a width proportionalto the width of a flaw along said scanning line, a source of oscillatoryvoltage, counting means for producing an indicating voltage in responseto a predetermined number of oscillations from the oscillatory voltagesource, and gating means connected to said oscillatory voltage sourceand responsive to pulses in said pulsed signal for coupling the outputof the oscillatory voltage source to said counting means for successivetime intervals which are proportional to the widths of the pulsesapplied thereto, whereby said indicating voltage will be produced whenthe sum of the widths of the applied pulses reaches a predeterminedamount.

4. The combination claimed in claim 3 and including means for resettingsaid counting means after the material has moved a predetermineddistance.

5. In apparatus for detecting flaws on the surface of moving material inwhich the flaws have a different optical appearance than the remainderof the material, the combination of means including an electron-opticsdevice for scanning an image of the surface of said body with anelectron beam at a sweep repetition frequency proportional to the speedof the moving material, means responsive to the output of saidelectron-optics device for producing a first pulsed signal in which eachpulse has a width proportional to the width of a flaw along saidscanning line, a source of oscillatory voltage, first counting means forproducing an indicating voltage in response to a predetermined number ofoscillations from the oscillatory voltage source, gating means connectedto said oscillatory voltage source and responsive to the pulses in saidpulsed signal for coupling the output from the oscillatory voltagesource to said first counting means for successive time intervals whichare proportional to the widths of the pulses applied thereto wherebysaid indicating voltage will be produced when the sum of the widths ofthe applied pulses reaches a predetermined amount, means for producing asecond pulsed signal having a pulse recurrence frequency proportional tothe speed of said moving material, a second counting means responsive tosaid second pulsed signal for producing a control voltage after apredetermined number of pulses in the second pulsed signal have beenapplied thereto, and means for applying said control voltage to saidfirst counting means to reset the same.

6. In an automatic hot scarfing machine for burning flaws from thesurface of heated steel slabs, the combination of conveyor means formoving a heated slab along a substantially straight line path, anelectron-optics device mounted above said path for scanning an image ofthe surface of a heated slab with an electron beam along a lineextending substantially perpendicular to the direction of movement ofthe slab, means responsive to the speed of said slab for controlling theelectron-optics device whereby the sweep repetition rate of its electronbeam is proportional to the speed of the slab, means coupled to theoutput of said electron-optics device for producing a pulsed signal inwhich each pulse has a width proportional to the width of a flaw scannedby said electron beam,

17 means for integrating the Widths of the pulses in said signal toproduce a control voltage when the sum of the widths of the pulses insaid signal reaches a predetermined amount, and means operable inresponse to said control voltage for rendering said scarfing machineoperative.

7. In an automatic hot scarfing machine for burning defects from thesurface of heated steel slabs, the combination of conveyor means formoving the heated slab along a substantially straight line path, anelectron-optics device mounted above said path for electronicallyscanning an image of a surface of a heated slab passing therebeneath,the sweep repetition rate of said electron-optics device beingproportional to the speed of said slab, apparatus coupled to saidelectron-optics device for producing a pulsed signal in which positivepulses are produced by defect images having a greater light intensitythan the remainder of the slab and negative pulses are produced bydefect images having a lesser light intensity than the remainder of theslab, the widths of said positive and negative pulses being proportionalto the defects which they represent, and means coupled to saidelectron-optics device for integrating the widths of the positive andnegative defect pulses in said signal to produce an indicating voltagewhen the sum of Widths of said positive and negative defect pulsesreaches a predetermined amount.

8. In an automatic hot scarfing machine for burning defects from thesurface of heated steel slabs, the combination of conveyor means formoving the heated slab along a substantially straight line path, anelectron-optics device mounted above said path for electronicallyscanning an image of the surface of a heated slab passing therebeneath,the sweep repetition rate of said'electronoptics device beingproportional to the speed of said slab, apparatus coupled to saidelectron-optics device for producing a pulsed signal in which positivepulses are pro duced by defect images having a greater light intensitythan the remainder of the slab and negative pulses are produced bydefect images having a lesser light intensity than the remainder of theslab, the widths of said positive and negative pulses being proportionalto the widths of the defects which they represent, means coupled to saidelectron-optics device for integrating the widths of the positive andnegative defect pulses in said signal to pro duce a first controlvoltage when the sum of the widths of said positive and negative defectpulses reaches a predetermined amount, means responsive to said pulsedsignal for producing a second control voltage when the amplitude ofnegative defect pulses in said pulsed signal reaches a predeterminedlimit, and means responsive to said first and second control voltagesfor rendering said scarfing machine operative whenever a control voltageis applied thereto.

9. In apparatus for automatically controlling a device for scarfing thesurface of a moving irradiant metal body on which flaws appear brighteror darker with respect to the remainder of the body, the combination ofan electron-optics device for scanning an image of the surface of saidbody with an electron beam at a sweep repetition frequency proportionalto the speed of the body to thereby produce a video signal in which eachscanning cycle of the electron beam produces a relatively long pulsehaving superimposed thereon positive and negative short pulses producedwhen the electron beam scans over flaw images, means responsive to saidvideo signal for producing a dilferentiated signal in which spikedpulses are produced at the leading and trailing edges of each pulse inthe video signal, means for eliminating the spiked pulses in saiddifferentiated signal which are due to the leading and trailing edges ofthe relatively long pulses in said video signal, a device responsive tothe output of said last-named means for producing a pulsed signal inwhich a pulse is formed between each pair of spikes formed by theleading and trailing edges of each short pulse in the original videowave form, a first source of oscillatory voltage, counting means forproducing a control voltage in re sponse to a predetermined number ofoscillations from said oscillatory voltage source, means responsive tosaid last-named pulsed signal for coupling the output of saidoscillatory voltage source to said counting means for successive timeintervals which are proportional to the widths of the successive pulsesin said last-named pulsed signal, and apparatus responsive to thecontrol voltage produced by said counting means for actuating saidscarfing device to remove a predetermined length of the surface of saidbody.

10; The combination claimed in claim 9 and including means for producinga second control voltage for actuating the scarfing device when theamplitude of negative short pulses in said video signal reaches apredetermined limit. l

11. In apparatus for automatically controlling a device for scarfing thesurface of a moving irradiant body on which flaws appear brighter ordarker with respect to the remainder of the body, the combination of anelectronoptics device for scanning an image of the surface of said bodywith an electron beam at a sweep repetition frequency proportional tothe speed of the body to thereby produce a video signal in Which'eachscanning cycle of the electron beam produces a relatively long pulsehaving superimposed thereon positive and negative short pulses producedwhen the electron beam scans over flaw images, means responsive to saidvideo signal for producing a differentiated signal in which spikedpulses are produced at the leading and trailing edges of each pulse inthe video signal, means for eliminating the spiked pulses in saiddifferentiated signal which are due to the leading and trailing edges ofthe relatively long pulses in said video signal, a device responsive tothe output of said last-named means for producing a third pulsed signalin which a pulse is formed between each pair of spikes formed by theleading and trailing edges of each short pulse in the original videowave form, a source of oscillatory voltage, first counting means forproducing a control voltage in response to a predetermined number ofoscillations from said oscillatory voltage source, means responsive tosaid third signal for coupling the output of said oscillatory voltagesource to said counting means for successive time intervals which areproportional to the Widths of the successive pulses in said thirdsignal, apparatus responsive to the control voltage from said countingmeans for actuating said scarfing device, means responsive to the speedof said body for producing a fourth pulsed signal having a pulserepetition frequency proportional to the speed of said body, secondcounting means responsive to the fourth pulsed signal for producing anindicating voltage pulse when the number of pulses in said fourth signalreaches a predetermined limit, and means for applying said indicatingvoltage pulse to said first counting means to reset the same.

12. In apparatus for detecting flaws on the surface of moving materialin which the flaws have a different optical appearance than theremainder of the material, the combination of means for generating asine wave signal having a frequency proportional to the speed of saidmoving material, apparatus responsive to said sine wave signal forgenerating a train of square wave voltage pulses having a pulserepetition frequency proportional to thevfrequency of said sine wave,means for scanning an image of the surface of said material with anelectron beam, apparatus coupled to said scanning means and responsiveto said train of square wave voltage pulses for sweeping said electronbeam across said image of the surface of said material at a recurrencefrequency proportional to the pulse repetition frequency of said trainof square wave voltage pulses, means coupled to the output of saidscanning means forproducing a pulsed signal in which each pulse has aWidth proportional to the width of a flaw on the surface of the materialscanned by said electron beam, and means coupled to said last-namedmeans for integrating the widths of the pulses in said pulsed signal topro duce an indicating voltage when the sum of the widths of the pulsesin said signal reaches a predetermined amount.

13. In apparatus for detecting flaws on the surface of moving materialin which the flaws have a different optical appearance than theremainder of the material, the combination of means for generating asine wave signal having a frequency proportional to the speed of saidmoving material, apparatus responsive to said sine wave signal forgenerating a train of square wave voltage pulses having a pulserepetition frequency proportional to the frequency of said sine wave,means for scanning an image of the surface of said material with anelectron beam, apparatus coupled to said scanning means and responsiveto said train of square wave voltage pulses for sweeping the electronbeam across said image of the surface of said material each time a pulseoccurs in said train of square wave voltage pulses, circuitry coupled tothe output of said scanning means for producing a pulsed signal in whicheach pulse has a width proportional to the width of a flaw on thesurface of the material scanned by said electron beam, a source ofoscillatory voltage, counting means for producing an indicating voltagein response to a predetermined number of oscillations from theoscillatory voltage source, and means responsive to the pulses in thepulsed signal produced by said circuitry for coupling the output of saidoscillatory voltage source to said counting means for successive timeintervals which are proportional to the widths of the pulses appliedthereto, whereby the said indicating voltage will be produced when thesum of the widths of the said applied pulses reaches a predeterminedamount.

14. In apparatus for detecting flaws on the surface of moving materialin which the flaws have a different optical appearance than theremainder of the material, the combination of means for generating asine wave signal having a frequency proportional to the speed of saidmoving material, apparatus responsive to said sine wave signal forgenerating a train of square wave voltage pulses having a pulserepetition frequency proportional to the frequency of said sine wave,means for scanning an image of the surface of said material with anelectron beam, apparatus coupled to said scanning means and responsiveto said train of square wave voltage pulses for sweeping said electronbeam across said image of the surface of said material each time a pulseoccurs in said train of square wave voltage pulses, circuitry coupled tothe output of said scanning means for producing a pulsed signal in whicheach pulse has a width proportional to the width of a flaw on thesurface of the material scanned by said electron beam, a source ofoscillatory voltage, first counting means for producing an indicatingvoltage in response to a predetermined number of oscillations from theoscillatory voltage source, means responsive to the pulses in the pulsedsignal produced by said circuitry for coupling the output of saidoscillatory voltage source to said counting means for successive timeintervals which are proportional to the widths of the pulses appliedthereto whereby the said ndicating voltage will be produced when the sumof the widths of the said applied pulses reaches a predetermined amount,second counting means, means for applying said train of square wavevoltage pulses to said second counting means whereby the counting meanswill produce a control voltage pulse in response to a predeterminednumber of voltage pulses in the train of square wave voltage pulses, andmeans for applying said control voltage pulse to said first countingmeans to reset the same.

References Cited in the file of this patent UNITED STATES PATENTS2,479,624 Jones et al Aug. 23, 1949 2,674,915 Anderson Apr. 13, 19542,756,627 Boychs July 31, 1956 2,803,755 Milford Aug. 20, 1957 2,868,059Summerhayes Jan. 13, 1959 2,910,908 Meyer Nov. 3, 1959

